1. Field of the Invention
The present invention relates to a one-way clutch used in a power transmission system in an automative vehicle or the like for the purpose of one-way torque transmission, prevention of a reverse rotation and the like, and more particularly relates to a retainer used in such a one-way clutch of the type described above.
2. Related Background Art
A one-way clutch is disposed between an inner race or driving race and an outer race or driven race so that when the driving race rotates in a predetermined direction, it transmits driving torque to the driven race, but when the direction of rotation of the driving race is opposite to the predetermined direction no driving torque is transmitted to the driven race.
Generally, one-way clutches may be divided into two types, a sprag type and a roller type.
A sprag type one-way clutch comprises an outer race having an annular inner surface, an inner race having an outer peripheral surface which is in coaxial and opposing relationship with the inner surface of the outer race and a plurality of sprags or wedges disposed in an annular space defined between the inner surface of the outer race and the outer surface of the inner race. When the inner race rotates in one direction, its upper and lower cam surfaces are inclined to positions at which no driving torque is transmitted and the relative movement between the inner and outer races is permitted. On the other hand, when the inner race is rotated in the opposite direction, the cam surface of each sprag is displaced so that the sprags are caused to rise and prevent the relative movement between the outer and inner races. Consequently, the driving torque is transmitted from the inner race to the outer race. The one-way clutch of the type described above is disclosed in, for instance, Japanese Patent Laid-Open No. 54-109557 (1979).
A common problem of older one-way clutches is that they have no facility for positioning in the axial direction in single one-way clutch assemblies. It follows therefore than when such a one-way clutch is mounted, a device capable of preventing the displacement in the axial direction of the one-way clutch must be mounted. A locating snap ring as shown in FIG. 7 and a retaining plate as shown in FIG. 8 are examples of devices for preventing the displacement in the axial direction of one-way clutches.
FIG. 7 is a sectional view of a conventional sprag type one-way clutch taken in the direction perpendicular to the axis thereof. An outer retainer 71 is in the form of a cylinder and is formed with 16 outer slots about a periphery thereof. An inner retainer 72 is also in the form of a cylinder smaller in diameter than the outer retainer 71, and is fitted into the outer retainer 71 coaxially thereof. Furthermore the inner retainer 72 is formed with a plurality of inner slots which are equal in number to the outer slots of the outer retainer 71 in radially opposing relationship with the outer slots of the outer retainer 71 and which are substantially similar in shape to the outer slots.
Sprags 73 (each in the form of a gourd when viewed from the axial direction of the retainer) are extended through the outer and inner slots, and the upper surface of each sprag 73 is arranged to contact with the inner peripheral surface of the outer race 75 while the lower surface thereof is arranged to contact with the outer peripheral surface of the inner race 76.
The inner peripheral surface of the outer race 75 is formed with an annular or circular groove 75a into which is fitted a locating snap ring 77. The ring 77 is thin and in the form of a ring whose peripheral part is partially cut off and is made of a spring material. The ends of the cut-off part are pressed against each other so that the diameter of the ring 77 is decreased when the ring 71 is fitted into the annular groove 75a. After being fitted into the annular groove 75a, the ring 75 springs back to its original diameter, and is pressed against the inner peripheral side surfaces and the bottom of the annular groove 75a.
When the outer retainer 71 is displaced in the axial direction, it engages with the locating snap ring 77 so that the further displacement of the outer retainer 71 is stopped. Thus the locating snap ring 77 functions as a stopper. As a result, the displacement of the sprags 73 and the inner retainer 72 can be prevented.
FIG. 8 is a sectional view of a conventional sprag type one-way clutch equipped with another means for preventing the displacement in the axial direction of the outer retainer, taken in the direction perpendicular to the axis of the one-way clutch. An outer retainer 81 is in the form of a cylinder and is formed with 16 outer slots about a periphery thereof. An inner retainer 82 is also in the form of a cylinder which is smaller in diameter than the outer retainer 81 and is fitted into the outer retainer 81 coaxially thereof. Furthermore, the inner retainer 82 is formed with a plurality of inner slots which are equal in number to the outer slots of the outer retainer 81 and substantially similar in shape to the outer slots. Sprags 83 (each in the form of a gourd when viewed from the axial direction of the retainer) are extended through the outer and inner slots. The upper surface of each sprag 83 is arranged to contact with the inner peripheral surface of the outer race 85 while the lower surface thereof is arranged to contact with the outer peripheral surface of the inner race 86.
A retaining platt 87 is attached to the open end of the outer race 85. The retaining plate 87 is thin and is similar in shape to the locating snap ring 77 shown in FIG. 7, but its outer peripheral portion has a caulked portion 87a caulked to the outer peripheral surface of the outer race 85, whereby the retaining plate 87 is securely attached to the outer race 85.
Like the locating snap ring 77 shown in FIG. 7, the retaining plate 87 engages with the outer retainer 81 when the latter is displaced axially and outwardly so that the retaining plate 87 also functions as a stopper. Therefore the displacement of the sprags 83 and the inner retainer 82 can be also prevented. However, in order to mount the locating snap ring or the retaining plate on the outer race, it is necessary that a space required for mounting the ring or plate must be previously selected on the outer race and its surrounding portion. Another problem is that since the locating snap rings or the retaining plates must be fabricated independently of the outer race, the overall fabrication costs are increased.
Furthermore, in the conventional one-way clutch of the type in which the inner race when and its retainer race, the rotational speed of the outer race varies suddenly, the sprags may temporarily slide relative to the raceway surface of the outer race due to force of inertia. This sliding of the sprags causes excessive wear of the raceway surface of the outer race and excessive wear of the sprags, so that the operating life of the one-way clutch is shortened. In order to prevent this effect, the outer retainer is, for formed with projections called drag pieces which in turn are forcibly made to contact with the outer race to produce strong frictional force.
In the case of the one-way clutch of the type described above, the design is such that in the case of idling or transmitting no torque, the race and sprags slide with respect to one another so that upon a change of the rotational input, a frictional force is directly exerted to each sprag, thereby changing its posture. With the above-described construction, some sprags are subjected to excessive wear. In addition, the posture change of all the sprags does not occur concurrently, in response to a sudden variation of the input. Therefore in order to concurrently and quickly change the positions of the sprags in response to a sudden variation in rotation input to the one-way clutch, and furthermore to prevent excessive wear of the sprags, projections called drag strips are projected from the inner race so as to produce weak friction between the inner race and the inner retainer, whereby the inner retainer can follow the variations in rotation of the inner race.
Furthermore, in the conventional one-way clutches, the inclination of the retainer with respect to the outer and inner races (that is, a misalignment between the retainer on one hand and the outer and inner races on the other hand) causes a malfunction of the clutch. In order to solve this problem at both sides of the retainer, ring-shaped portions which are equal in diameter to, for instance, the inner diameter of the outer race or the outer diameter of the inner race, must be provided.